Method for contactless transmission of information using two carrier waves and an intermediate side band on the carrier waves

ABSTRACT

A method for the contactless transmission of information between a transmitter/receiver unit and a transponder. The transmitter/receiver unit is caused to transmit a first and a second carrier wave which have mutually different frequencies (f1, f2), forming the difference frequency, of the two different frequencies ,in the transponder, dividing the third signal, (the difference frequence) (f3) to a fourth signal (f4) having half the difference frequency, causing the fourth signal to modulate the two carrier waves received in the transponder as a result of being applied to a diode or like device, so that the received carrier waves are reflected back from the transponder to the transmitter/receiver unit, mixing the signal received back in the transmitter/receiver unit with one of the first or the second carrier wave frequencies, and bringing forward each of the two sidebands on respective sides of the carrier wave frequency with which mixing is effected, such sidebands differing from the last mentioned carrier wave frequency by a frequency which is equal to half the difference frequency (f4), that sideband of the sidebands which has a frequency that lies between the carrier wave frequencies is a combined or combination sideband which is caused to have an amplitude that differs from the amplitude of the other sideband, and the pair of sidebands then being filtered and the information content of the sidebands being detected in the detecting circuit of the transmitter/receiver unit.

FIELD OF THE INVENTION

The present invention relates to a method for the contactlesstransmission of information.

BACKGROUND OF THE INVENTION

The Swedish Patent Specification No. (Swedish Patent Application8802230-6), having a corresponding U.S. Pat. No. 5,251,235, describesapparatus for the contactless transmission of information over a serialtwin-cable data bus, comprising a clock line and a data line connectedto a transmitter, a receiver and a demodulator. The transmitter includesan oscillator and a modulator which is intended to modulate the signalgenerated by the oscillator in response to the clock line signals anddata line signals respectively. The invention defined in said PatentSpecification is characterized in that the modulator is constructed tocarry out on the signal generated by the oscillator two significantlyseparated modulation steps which do not coincide in time, therewith toform two mutually independent signal channels, of which a first isintended for data signals and the other is intended for the clocksignals. The demodulator is constructed to demodulate signals which arereceived by the receiver and which have been modulated in the aforesaidmanner and also to recreate said two signals. The demodulator has aclock-line output and a data-line output.

The aforesaid Patent Specification defines a method of separating dataand clock lines, by using pauses in transmission as informationcarriers, wherewith, e.g., switching or marking of levels in the clockline triggers a first modulation step, which constitutes a shorttransmission pause, whereas switching or marking of levels in the dataline triggers a second modulation step which constitutes two rapid,sequential transmission pauses.

SUMMARY OF THE INVENTION

The present invention provides a novel and useful method for applicationin such data buses or other data links, such as to enable the signalstransmitted from the master side to be used as control oscillators onthe slave side, and therewith to enable the slave side to transmitsignals which are received on the master side without the signalstransmitted from said master side disturbing the reception of thesignals, transmitted from the slave side and without the occurrence ofzero settings, or so-called nodes, in the signal from the slave side.

The present invention thus relates to a method for the contactlesstransmission of information between a transmitter/receiver unit and atransponder, the transmitter/receiver unit comprising oscillators,transmitter and receiver antennas, a modulator and a detection circuit,and the transponder including a transmitter/receiver antenna, amodulator and a detection circuit. The invention is characterized inthat the transmitter/receiver unit is caused to transmit a first and asecond carrier wave which have mutually different frequencies (f1, f2);in that the difference frequency is formed in the transponder; in that athird signal having the difference frequence (f3) is caused to bedivided to a fourth signal having half the difference frequency (f4); inthat the fourth signal is caused to modulate the two carrier wavesreceived in the transponder by being applied to a diode or like device,such that the received carrier waves are reflected back to thetransmitter/receiver unit; in that the signal received in thetransmitter/receiver unit is mixed down with one of the first or thesecond carrier wave frequencies; and in that each of the two sidebandson respective sides of the carrier wave frequency with which said mixingis effected are brought forward, said sidebands differing from the lastmentioned carrier wave frequency by a frequency which is equal to halfthe difference frequency (f4), wherein that sideband of said sidebandswhich has a frequency that lies between the carrier wave frequencies isa combined sideband which is caused to have an amplitude which differsfrom the amplitude of the other sideband, and wherein the pair ofsidebands are filtered and the information content of the sidebandsdetected in the detecting circuit of the transmitter/receiver unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference toexemplifying embodiments thereof illustrated in the accompanyingdrawing, in which

FIG. 1 illustrates a transmitter/receiver unit;

FIG. 2 illustrates a transponder; and

FIG. 3 illustrates a frequency diagram.

DESCRIPTION OF THE INVENTION

It will be evident from the following that the present invention can beapplied in the most widely varying two-directional information links. Itwill also be understood that the invention is not restricted to theillustrated embodiment of apparatus and that said embodiment shall beseen solely as a means of explaining the inventive method.

It is assumed in the illustrative embodiment that the link or the busoperate at microwave frequencies, although the invention is notrestricted to these frequency bands, but can be applied at otherfrequency bands.

FIGS. 1 and 2 illustrate schematically a transmitter/receiver unit 1,hereinafter called the transmitter, and a transponder 2. These units 1,2 form a link by means of which information, e.g. data, can betransmitted in both directions. The transmitter 1 includes, among otherthings, oscillators 3, 4, transmitter and receiver antennas 5, 6, 7, amodulator 8, and a detection circuit 9. The transponder 2 includes,among other things, a transmitter/receiver antenna 10, a modulator 11,12 and a detection circuit 13.

The transmitter 1 also includes mixers 14-16, bandpass filters 17, 25,amplifiers 18, 19, a rectifier 20 and a summation circuit 21. Thetransponder 2 further includes a circuit 22 which is intended to formthe difference frequency between two frequencies, and a frequencydivider 23. Depending on the field of use, the transponder may alsoinclude a memory store 24, which may be constructed to deliverinformation and also to receive information and to store the informationreceived.

According to the present invention, the transmitter is caused totransmit a first and a second carrier wave of mutually differentfrequencies (f1, f2). This is illustrated in FIG. 1, in that theoscillator 3 is shown to generate a signal having a frequency of 2450MHz, which is sent to the antenna 6. The signal is also sent to a mixer15, to which there is also applied a signal from a further oscillator 4,which in the illustrated case generates the frequency 13.5 MHz. Themixer 15 is constructed so that a signal having the frequency 2463.5 MHzwill appear on its output when the oscillator 4 is activated by themodulator 8. This signal is sent along the lines 30-31 to the antenna 6.Thus, a first and a second signal in the form of two carrier waves aretransmitted by means of the antenna 6.

This transmitted signal is received in the transponder 2 on the antenna10. As before mentioned, the transponder includes a circuit 22 which isintended to form the difference frequency between the two carrier wavefrequencies. Thus, there is formed in the transponder 2 a third signalwhich has the difference frequency formed in the circuit 22.

The frequency divider 23 in the transponder is operative to divide thethird signal having the difference frequency (f3) into a fourth signalof half the difference frequency (f4).

The fourth signal is caused to modulate the two carrier waves receivedin the transponder, by being applied to a diode or like device in themodulator 12, so that the received carrier waves will be reflected backvia transponder antenna 10 to the transmitter 1, without supplyingfurther energy to the carrier waves.

The modulator in the transponder also includes a circuit 11 which isoperative to start and stop the modulation step in accordance with theinformation to be transmitted from the transponder 2 to the receiver 1.This information can be delivered to the circuit 11 from a memory store24, or alternatively from a data line 32. Thus, the two carrier wavesare transmitted from the transponder, each modulated with a frequency f4which is equal to half the difference frequency between the carrier wavefrequencies.

According to the inventive method, the signal received on the antenna 5of the transmitter 1 is mixed with the frequency of the first or thesecond carrier waves in a mixer 14 intended therefor. The two sidebandson respective sides of the carrier wave frequency with which said mixingis effected is the output signal from the mixer 14. These two sidebandsdiffer from the last mentioned carrier wave frequency by a frequencywhich is equal to half the difference frequency (f4).

FIG. 3 illustrates a frequency diagram in which the transmitted carrierwaves have been designated f1 and f2 respectively. If mixing-down in themodulator 14 is effected with the frequency 2450 MHz, the sidebandswhose frequencies differ from 2450 MHz by 6.75 MHz will therefore liedownstream of the mixer 14.

However, the other carrier wave in the transponder having half thedifference frequency is also modulated, and consequently this carrierwave with associated pair of corresponding sidebands will be received inthe receiver. One of these last mentioned sidebands has a frequencywhich is 6.75 MHz higher than the frequency of the other carrier wave, afrequency of 2463.5 MHz, and the other of said sidebands has a frequencywhich is 6.75 MHz lower than 2463.5 MHz.

Because modulation is effected in the transponder with half thedifference frequency, that particular sideband of the occurringsidebands which has a frequency centrally between the carrier wavefrequencies will be a combined or combination sideband.

According to the invention, the combined sideband is given an amplitudewhich differs from the amplitude of the other, filtered sideband, asillustrated in FIG. 3. According to the invention, the combined sidebandand said other sideband are filtered-out with the aid of the bandpassfilter 17.

Two methods and combinations therebetween can be employed to ensure thatthe combined sideband will have an amplitude which differs from theother sideband.

One method is to permit the carrier waves to have a sufficiently largeamplitude difference, for example a difference factor of at least about2.

Another method is to permit the carrier waves to have the same amplitudebut to cause the signal which modulates the carrier waves in thetransponder to have a phase which is different to the phase of thatsignal which is frequency-halved and mixed-down in the transponder, i.e.the aforesaid fourth signal.

By combinations of these methods is meant that both amplitudes andphases can be varied, wherewith the amplitude difference between thecarrier waves need not longer be in the order of twice the difference.

Irrespective of how amplitudes and phases are selected, it shall beensured that the three sidebands, namely the two sidebands which formthe combined sideband and said other sideband, do not have vectors in anamplitude-phase diagram which give resultants which are equal to zerosubsequent to mixing in the transmitter/receiver unit.

The fact that the central sideband has an amplitude which is differentto the other sideband of the sideband pair results in that no zeropositions, or nodes, can occur in the received signal as a result ofinterference or disturbance.

The filtered sideband, or pair of sidebands, is detected in thedetection circuit 9 of the transmitter with respect to the informationcontent of the sidebands. The circuit 20 is a rectifier.

The signal appearing on the output of the rectifier 20 is therefore adata signal. The clock frequency in the transmitter is 13.5 MHz, and theclock signal can be taken from the oscillator 4, through an output.

The clock signal in the transponder 2 also has a frequency of 13.5 MHzand is taken from the circuit 22 via a line 33, so as to control, interalia, the infeed and outfeed of data into and from the memory store 24,if a store is included, and to control the modulator 11. Consequently,no oscillator is required in the transponder, either to produce amodulation signal or to produce a control oscillator signal.

The transmitter is also able to transmit information to the transponder.In this case, the modulator 8 is used to control, e.g. the oscillator 4in a manner such that, e.g., the transmission pause takes place inaccordance with what is described in the aforesaid patent specification,i.e. transmission pauses which corresponds to the information to betransmitted to the transponder. It will be understood that thetransponder may also operate in accordance with the principle ofmodulating by means of the transmission pause.

A signal received in the transponder is detected in the transponderdetection circuit, where the signal f3 having the difference frequencyis supplied to the detection circuit, where, e.g., transmission pausesare detected while the clock frequency in the transponder is thedifference frequency, as before mentioned.

One output 34 of the transponder detection circuit 13 may concern dataand one output 35 may concern the clock. The transponder may also be soconstructed that the information recovered by means of the detectioncircuit is fed into the memory 24 of the transponder, via a line 36. Thereference numeral 32 identifies a further input direct to the memory.

According to one preferred embodiment of the invention, the signalreceived in the transmitter is also mixed-down with the other of thecarrier wave frequencies f2. This is effected in the same manner as thatdescribed with reference to the frequency f1. The transmitter herewithincludes a further mixer 16 on the output of which there appears acorresponding pair of sidebands which differ mutually with a frequencyof 13.5 MHz. The two sidebands, each on respective sides of the carrierwave frequency with which said mixing is effected, are filtered out in abandpass filter 25, which corresponds to the bandpass filter 17.Subsequent to being amplified in an amplifier 19, the signals arerectified in the circuit 20.

Two receiving channels are formed in this embodiment, namely onereceiving channel which includes a pair of sidebands around the firstcarrier wave and a receiving channel which includes a pair of sidebandsaround the other carrier wave. Subsequent to rectification in therectifier 20, the rectified signals are summated in the summationcircuit 21. Such a signal is much smoother than when solely onereceiving channel is used.

According to another preferred embodiment, the two carrier waves aretransmitted at different strengths. As a result, the different sidebandswill have different amplitudes, which in turn results in smallerfluctuations in the received signal. According to a further preferredembodiment, the transmitted carrier waves have a microwave frequency,preferably a frequency of 2450 MHz and a frequency of 2450 MHz plus orminus said difference frequency, said difference frequency preferablybeing 13.5 MHz.

It will be obvious that the present invention affords the advantagesrecited in the introduction.

In the aforegoing, the inventive method has been described withreference to specific embodiments thereof. It will be understood,however, that the apparatus used may have different constructions,depending on the field of use concerned, and that the same function canbe achieved with another detailed solution than that illustrated in thedrawing.

The present invention shall not therefore be considered restricted tothe illustrated, exemplifying embodiment, since modifications andvariations can be made within the scope of the following claims.

We claim:
 1. A method for the contactless transmission of informationbetween a transmitter/receiver unit and a transponder, wherein thetransmitter/receiver unit includes oscillators, transmitter and receiverantennas and a modulator and detection circuit, and wherein thetransponder includes a transmitter/receiver antenna, a modulator and adetection circuit, the method comprising the steps of: generating andtransmitting from the transmitter/receiver unit first and second carrierwave signals, which have mutually different frequencies (f1, f2), to thetransponder; receiving said first and second carrier wave signals by thetransponder; creating a third signal, which is the difference frequencyof said first and second carrier waves, in the transponder; dividing thethird signal (f3) and thereby creating a fourth signal having half thesaid difference frequency (f4); modulating the fourth signal with theinformation received by the transponder; modulating the two carrierwaves received in the transponder with the modulated fourth signal byapplying the modulated fourth signal and said received first and secondcarrier wave signals to a diode device, wherein the received carrierwaves are reflected back to the transmitter/receiver unit; mixing downthe carrier wave signals received back in the transmitter/receiver unitfrom the transponder, with one of the first and the second originalcarrier wave frequencies to thereby create a signal comprising onesideband on each of the respective sides of the carrier wave frequencywith which said mixing is effected; said sidebands differing from saidone of the first and the second original carrier wave frequencies by afrequency which is equal to half the difference frequency (f4), whereinone sideband, of said two sidebands, has a frequency that lies betweenthe said two carrier wave frequencies and is a combined sideband havingan amplitude which differs from the amplitude of the other of said twosidebands; filtering both sidebands and detecting the informationcarried by the sidebands in the detecting circuit of thetransmitter/receiver unit.
 2. A method according to claim 1, whereinsaid difference frequency (f3) is utilized as a clock frequency in saidtransponder.
 3. A method according to claim 1, wherein the signals ofboth the first and the second carrier wave frequencies received back inthe transmitter/receiver unit from the transponder are mixed with theother of the first and the second carrier wave frequencies, therewithproducing the two sidebands on respective sides of said other carrierwave frequency with which said mixing is effected, these sidebandsdiffering from the said other carrier wave frequency by a frequencywhich is equal to half the difference frequency (f4), therewith formingtwo receiving channels in said transmitter/receiver unit.
 4. A methodaccording to claim 3, including the further steps of rectifying andsummating the two receiving channels each of which include a pair ofsidebands around respective carrier wave frequencies.
 5. A methodaccording to claim 1, including the step of transmitting the two carrierwaves at different strengths.
 6. A method according to claim 1,including the steps of forming the difference frequency (f3) in thetransmitter/receiver unit, modulating said two carrier waves with thisdifference frequency, and detecting said third signal having thedifference frequency with respect to its information in the detectioncircuit of the transponder.
 7. A method according to claim 1, whereinsaid two transmitted carrier waves have microwave frequencies, of 2450MHz and a frequency of 2450 MHz plus or minus said difference frequencyrespectively, said difference frequency being 13.5 MHz.